To prevent unauthorized duplication or alteration of documents, frequently there is special indicia or a background pattern provided for sheet materials such as tickets, checks, currency, and the like. The indicia or background pattern is imposed upon the sheet material usually by some type of printing process such as offset printing, lithography, letterpress or other like mechanical systems, by a variety of photographic methods, by xeroprinting, and a host of other methods. The pattern or indicia may be produced with ordinary inks, from special inks which may be magnetic, fluorescent, or the like, from powders which may be baked on, from light sensitive materials such as silver salts or azo dyes, and the like. Most of these patterns placed on sheet materials depend upon complexity and resolution to avoid ready duplication. Consequently, they add an increment of cost to the sheet material without being fully effective in many instances in providing the desired protection from unauthorized duplication or alteration.
Various methods of counterfeit-deterrent strategies have been suggested including Moire-inducing line structures, variable-sized dot patterns, latent images, see-throughs, bar-codes, and diffraction based holograms. However, none of these methods employs a true scrambled image or the added security benefits deriving therefrom.
This same inventor earlier disclosed a novel system for coding and decoding indicia on printed matter by producing a parallax panoramagram image. These principles and embodiments of U.S. Pat. No. 3,937,565, issued Feb. 10, 1976 are hereby incorporated by reference. The indicia were preferably produced photographically using a lenticular line screen (i.e. a lenticular screen) with a known spatial lens density (e.g. 69 lines per inch). A specialized auto-stereoscopic camera might be used to produce the parallax image such as the one described in this inventor's U.S. Pat. No. 3,524,395, issued Aug. 18, 1970, and U.S. Pat. No. 3,769,890, issued Nov. 6, 1973.
Photographic, or analog, production of coded indicia images has the drawback of requiring a specialized camera. Also, the analog images are limited in their versatility in that an area of scrambled indicia is generally noticeable when surrounded by non-scrambled images. Also, it is difficult to combine several latent images, with potentially different scrambling parameters, due to the inability to effectively re-expose film segments in generating the scrambled, photographic image.
Systems such as described in U.S. Pat. Nos. 3,937,565; 3,769,890; 4,092,654; 4,198,147; and 4,914,700 disclose methods of preventing counterfeiting by forming a parallax panoramagram image of a subject, known as Scrambled Indicia® system, typically photographically through a lenticular line screen (i.e. a lineticular screen).
Scrambled images resist ready reproduction by photographic or xerographic techniques inasmuch as the extent of scrambling or encoding provided by these system is controlled by a large variety of parameters peculiarly under the control of the originator of the scrambled or encoded image. Yet, the scrambled image can be unscrambled for visual examination using a decoder that is substantially a duplicate of the lenticular screen used to form the original image.
The systems and methods described in the above-identified prior art patents typically employ an autosteroscopic camera for photographing artwork so as to produce a scrambled parallax panoramagram thereof. Specifically, the camera includes a lenticular screen and a photosensitive element is placed in the combined image plane of the camera formed by the objective lens and the lenticular screen. The image of the graphic to be encoded is focussed on the photosensitive element in the image plane of the camera with a small aperture stop that increases the depth of focus. The lenticular screen and photosensitive element are then moved longitudinally along the optical axis of the camera with respect to the objective lens of the camera to one edge of, but within the limits defining, the depth of focus. The photosensitive element is then exposed to the light projected from the graphic while the lenticular screen and photosensitive element are moved together laterally relative to the objective lens of the camera to expose successive portions of the photosensitive element underlying the screen. The relative movements are such that the point image of the subject center of the graphic will be recorded in the center of the photosensitive element as a blurred spot which is moved progressively in the course of the relative movement of the objective lens, lenticular screen, and photosensitive element.
The resulting image formed on the photosensitive element is a lenticular dissection of the image of the graphic, as well as an image in which the displacement between the subject center and the second conjugate point introduces a scrambling factor so that the scrambled or encoded image cannot readily be identified by unaided vision.
As an alternative security printing system, diffraction-based images such as embossed holograms have been incorporated into the surface of credit cards and the like. Although this tactic initially reduced the incidence of forgeries, the technology for reproducing and incorporating embossed holograms has become sufficiently widespread that its use in preparing security devices has been impaired.
Another optical documentary security and object authentication device is the optically variable device, such as a KINEGRAM®, available from Landis & Gyr communications (Switzerland) Corp., which another diffraction-based system that can be fabricated using an embossing technique and presents distinctive dynamic optical effects easily visualized by an observer. The system is suggested for use as a high-level optical security device to protect banknotes, passports, Visas, ID-cards, and other security documents against counterfeit and tampering. The image of a KINEGRAM® is created by a plurality of invisibly small elementary areas of reflective micro-profiles, each of which diffract illuminating light. The elementary areas are used to compose lines and graphical elements. For each area or line element, micro-profile size and shape, the angles of diffraction and diffraction intensities are calculated to produce the overall image.
Accordingly, a method and apparatus are needed whereby the photographic process and its results are essentially simulated digitally via a computer system and related software. Additionally, a system is needed whereby scrambled latent images can be integrated into a source image, or individual color components thereof, so that the source image is visible to the unaided eye and the latent image is visible only upon decoding. Also needed is the ability to incorporate multiple latent images, representing different “phases”, into the source image for added security.